The present invention relates to down-hole drill strings, and more particularly to devices for channeling working fluid within such drill strings.
Many deep-hole drilling applications require large volumes of air to provide ample hole cleaning velocity and “cuttings lift”. Proper drill performance necessitate removal of cuttings from a work hole as they are produced by the drill to maintain a “clean” hole and prevent plugging or loss of fluid circulation. While working fluid, such as compressed air, is normally expelled at the bottom of the hole, it is also desirable to expel or discharge fluid at various depths in the work hole where supplemental fluid flow/velocity may be beneficial. However, there are generally limitations as the quantity or volume of fluid that can be circulated with a down-hole drill (“DHD”) due to the internal geometry or structure of the DHD. Additionally, drill performance will be negatively affected by excessive internal backpressure that generally results from bypassing flow to create such supplemental flow. Further, most DHD's must be taken apart to make flow adjustments, which is usually a time consuming process that should only be performed by qualified service staff.
Furthermore, commercially available devices commonly referred to as “Jet Subs” are known for providing such desired air flows. However, these devices are rather complex, require incorporation of a separate device into the drill string, and prone to failure and thus generally unreliable. For example, these devices typically include throttle orifices that are protected from back-flow (to prevent debris from entering the clean high pressure air supply) with a spring check valve. Such check valves often break and allow contamination into the drill string.